scholarly journals Multivalent polyglycerol supported imidazolidin-4-one organocatalysts for enantioselective Friedel–Crafts alkylations

2015 ◽  
Vol 11 ◽  
pp. 730-738 ◽  
Author(s):  
Tommaso Pecchioli ◽  
Manoj Kumar Muthyala ◽  
Rainer Haag ◽  
Mathias Christmann
Keyword(s):  
Catalytic System ◽  
First Generation ◽  
High Loading ◽  
Turnover Rates ◽  
Selective Precipitation ◽  
Unsaturated Aldehydes ◽  
Cuaac Reaction ◽  
Hyperbranched Polyglycerol

The first immobilization of a MacMillan’s first generation organocatalyst onto dendritic support is described. A modified tyrosine-based imidazolidin-4-one was grafted to a soluble high-loading hyperbranched polyglycerol via a copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction and readily purified by dialysis. The efficiency of differently functionalized multivalent organocatalysts 4a–c was tested in the asymmetric Friedel–Crafts alkylation of N-methylpyrrole with α,β-unsaturated aldehydes. A variety of substituted enals was investigated to explore the activity of the catalytic system which was also compared with monovalent analogues. The catalyst 4b showed excellent turnover rates and no loss of activity due to immobilization, albeit moderate enantioselectivities were observed. Moreover, easy recovery by selective precipitation allowed the reuse of the catalyst for three cycles.

scholarly journals Synthesis of a tyrosinase inhibitor by consecutive ethenolysis and cross-metathesis of crude cashew nutshell liquid

2018 ◽  
Vol 14 ◽  
pp. 2737-2744 ◽  
Author(s):  
Jacqueline Pollini ◽  
Valentina Bragoni ◽  
Lukas J Gooßen
Keyword(s):  
First Generation ◽  
Anacardic Acid ◽  
Side Chain ◽  
Tyrosinase Inhibitor ◽  
Target Compound ◽  
Selective Precipitation ◽  
Acid Component ◽  
Cross Metathesis ◽  
Cashew Nutshell Liquid ◽  
Bond Isomers

A convenient and sustainable three-step synthesis of the tyrosinase inhibitor 2-hydroxy-6-tridecylbenzoic acid was developed that starts directly from the anacardic acid component of natural cashew nutshell liquid (CNSL). Natural CNSL contains 60–70% of anacardic acid as a mixture of several double bond isomers. The anacardic acid component was converted into a uniform starting material by ethenolysis of the entire mixture and subsequent selective precipitation of 6-(ω-nonenyl)salicylic acid from cold pentane. The olefinic side chain of this intermediate was elongated by its cross-metathesis with 1-hexene using a first generation Hoveyda–Grubbs catalyst, which was reused as precatalyst in a subsequent hydrogenation step. Overall, the target compound was obtained in an overall yield of 61% based on the unsaturated anacardic acid content and 34% based on the crude CNSL.

MOFs-Derived Co@CN bi-functional catalysts for selective transfer hydrogenation of α,β-unsaturated aldehydes without use of base additives

2017 ◽  
Vol 1 (10) ◽  
pp. 2005-2012 ◽  
Author(s):  
Xiaomei Liu ◽  
Shujuan Cheng ◽  
Jilan Long ◽  
Wei Zhang ◽  
Xiaohong Liu ◽  
...  
Keyword(s):  
Noble Metal ◽  
Catalytic System ◽  
Transfer Hydrogenation ◽  
Unsaturated Aldehyde ◽  
Selective Transfer ◽  
Unsaturated Aldehydes ◽  
Highly Efficient

A highly efficient non-noble metal catalytic system for selective transfer hydrogenation of an α,β-unsaturated aldehyde without use of alkaline additives was developed.

Selective Hydrogenation of α,β-Unsaturated Aldehydes on Ru-Sn/TiO2 Catalysts

2003 ◽  
Vol 68 (10) ◽  
pp. 1927-1936 ◽  
Author(s):  
Jana Špringerová ◽  
Petr Kačer ◽  
Jan Hájek ◽  
Libor Červený
Keyword(s):  
Catalytic Activity ◽  
Catalytic System ◽  
Catalytic Hydrogenation ◽  
Selective Hydrogenation ◽  
Carbonyl Compounds ◽  
Sol Gel ◽  
Positive Influence ◽  
Gel Method ◽  
Unsaturated Ketones ◽  
Unsaturated Aldehydes

Selective catalytic hydrogenation of unsaturated carbonyl compounds was studied on bimetallic Ru-Sn/TiO2 catalysts. The catalysts were prepared by a sol-gel method and co-impregnation in order to evaluate selected parameters (amount of the modifying tin, TiO2 support - commercial, standard sol-gel, modified sol-gel) on their catalytic activity and selectivity. Significant tin effect was proved especially with regard to the positive influence on selectivity. Sol-gel modified TiO2 was found to be the optimum support. Furthermore, the effect of substrate was studied. The suitability of the catalytic system for hydrogenation of unsaturated aldehydes was proved but it is not suitable for selective hydrogenation of unsaturated ketones.

Colloidal systems in soils

1994 ◽  
Vol 52 ◽  
pp. 64-65
Author(s):  
J. Thieme ◽  
J. Niemeyer ◽  
P. Guttman
Keyword(s):  
Clay Minerals ◽  
Polymeric Materials ◽  
Spatial Arrangement ◽  
High Specific Surface Area ◽  
Turnover Rates ◽  
Colloidal Systems ◽  
Chemical Conditions ◽  
Aggregation Phenomena ◽  
Iron And Manganese ◽  
Soil Colloids

In soil science the fraction of colloids in soils is understood as particles with diameters smaller than 2μm. Clay minerals, aquoxides of iron and manganese, humic substances, and other polymeric materials are found in this fraction. The spatial arrangement (microstructure) is controlled by the substantial structure of the colloids, by the chemical composition of the soil solution, and by thesoil biota. This microstructure determines among other things the diffusive mass flow within the soils and as a result the availability of substances for chemical and microbiological reactions. The turnover of nutrients, the adsorption of toxicants and the weathering of soil clay minerals are examples of these surface mediated reactions. Due to their high specific surface area, the soil colloids are the most reactive species in this respect. Under the chemical conditions in soils, these minerals are associated in larger aggregates. The accessibility of reactive sites for these reactions on the surface of the colloids is reduced by this aggregation. To determine the turnover rates of chemicals within these aggregates it is highly desirable to visualize directly these aggregation phenomena.

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